1. Field
Exemplary embodiments of the present disclosure relate to a fixing device and an image forming apparatus including the fixing device, and more specifically, a fixing device that fixes an image on a recording medium passing through a nip formed between a heat conductive member and a pressing member via an endless belt, and an image forming apparatus including the fixing device.
2. Description of the Background Art
Related-art image forming apparatuses, such as copiers, facsimile machines, printers, or multifunction apparatuses having at least one of copying, printing, scanning, and facsimile functions, typically form an image on a recording medium according to image data. In such an image forming apparatus, for example, a charger uniformly charges a surface of an image carrier; an optical writer emits a light beam onto the charged surface of the image carrier to form an electrostatic latent image on the image carrier according to the image data; a development device supplies toner to the electrostatic latent image formed on the image carrier to make the electrostatic latent image visible as a toner image; the toner image is directly transferred from the image carrier onto a recording medium or is indirectly transferred from the image carrier onto a recording medium via an intermediate transfer member; a cleaner then cleans the surface of the image carrier after the toner image is transferred from the image carrier onto the recording medium; finally, a fixing device applies heat and pressure to the recording medium bearing the toner image to fix the toner image on the recording medium, thus forming the image on the recording medium.
For image forming apparatuses, different types of fixing devices are proposed. For example, a heat-roller type fixing device has a pressing roller and a fixing roller including a heat source. The pressing roller is pressed against the outer circumferential surface of the fixing roller to form a nip between them. In such a state, when a recording medium bearing an unfixed toner image passes through the nip, heat and pressure are applied to the recording medium at the nip to fix the toner image on the recording medium. In addition, a belt-type fixing roller is proposed to include an endless fixing belt extended between a heat roller and a fixing roller. From the outer surface of the fixing belt, the pressing roller is pressed against the fixing roller.
Furthermore, a fixing device is proposed to include a stationary member in sliding contact with the inner surface of a rotary member. For example, JP-H04-044075-A proposes a film-heating type fixing device, and JP-H10-213984-A proposes a pressing-belt type fixing device. However, a film-heating type fixing device like that described in JP-H04-044075-A has limitations in durability of a fixing belt and stability of the temperature of the fixing belt. For a pressing-belt type fixing device like that described in JP-H10-213984-A, a large heat capacity of fixing roller may increase the time required for raising the temperature of the fixing roller, thus increasing the warm-up time.
To deal with such a challenge, for example, JP-2007-334205-A proposes a fixing device including a fixing belt and a pipe-shaped heat conductive member. The heat conductive member is fixedly mounted within a loop formed by the fixing belt so as to be able to guide the circulation of the fixing belt. A heat source is disposed within the heat conductive member to heat the fixing belt via the heat conductive member.
Such a configuration can shorten the warm-up time of the fixing device. In addition, the pipe-shaped heat conductive member diffuses heat to uniformly heat the entire fixing belt, thus stabilizing the temperature of the entire fixing belt.
However, for the fixing device, since a plurality of halogen heaters is arranged side by side in contact with each other in the circumferential direction of the fixing belt, there is a dead angle at which a portion of radiation heat emitted from one halogen heater is blocked by the other halogen heater. In such a dead angle, a portion of the amount of heat from one halogen heater for heating the metal heat-conductive member is absorbed by the other halogen heater, thus preventing optimization of heating efficiency.
Further, detecting the temperature of the fixing belt in such a dead angle by a temperature detector (e.g., thermistor) is disadvantageous in terms of responsiveness and sensitivity. As a result, although the fixing device can shorten the warm-up time, the fixing belt might be overheated if, for example, continuous activation of the heater occurs due to a failure of the fixing device. In addition, for example, JP-2007-334205-A has no description of the relative positions of the temperature detector and a clearance between the fixing belt and the heat conductive member.